Rather than being organised into starters and mains, the menu at Palate restaurant in Melbourne is separated into six proteins and 15 vegetables. Ivy Thompson beckons the waiter. “I’ll have the herbed chicken breast,” she says, “and the grilled tomato, smashed avocado, sweet potato mash and sautéed spinach.”

Palate launched its Paleo menu in 2011, the same year Thompson started her Paleo diet. “I was 29 and had just had my third child in three years. I wasn’t happy with my weight, and I was suffering from chronic illnesses.”

Thompson came to her new eating regime via the blog Mark’s Daily Apple. Mark Sisson, a former endurance athlete from the US, promotes a “primal diet” based on what humans supposedly ate before food became civilised. It’s heavy on meat, nuts, fruit, vegetables and eggs, and there’s minimal dairy, wheat, starch and processed carbohydrates. Within a month, Thompson had read all of Sisson’s blog posts, as well as his book, which promises “effortless weight loss, vibrant health and boundless energy”. His diet appealed to Thompson’s deeply rooted perfectionism. “There were so many rules that every day became like a test. And everything I do, I go hard.”

Thompson gave up all carbs and started her own blog, Paleo in Melbourne. In the first six months, Thompson shed weight and her energy levels peaked. Her blog grew in popularity, and she began to run workshops teaching others – mainly young mothers – how to source food that hadn’t been refined, boxed, tinned, canned or radically changed from its “natural state”. Her dedication was fanatical. At Christmas dinner she refused to eat anything but turkey and salad, and even that was difficult: “I sat there worrying whether the turkey was prepared with MSG.”

After a year of strict Paleo, Thompson noticed that she had put on weight around her stomach, but nowhere else. Troubled, she went to see her GP. “I told the doctor that I felt fantastic all the time,” Thompson recounts. “The doctor told me that feeling fantastic all the time is a warning sign, that I was high off adrenaline.”

The extreme physical reaction forced her to consider whether the diet had become an unhealthy obsession, and whether her body had become the signifier of a dysfunctional psychological state. “I’ve never had a relaxed relationship with food,” Thompson says. “It’s got nothing to do with other people’s rules. It’s all up here.” She points to her head. “I thought that I would never have to think about food again. But really I was thinking about food more than ever. I was replacing one obsession with another.”

Orthorexia nervosa, a term coined by Dr Steven Bratman, refers to an obsessive fixation with eating proper food. (The term “ortho” means straight or correct.) Bratman developed the concept in the mid 1990s while practising alternative medicine on the US west coast. Some of his patients were so restrictive with their diet that it struck him as a manifestation of a deeper psychological issue. “They would come in and ask me, ‘What food group should I cut out today?’ And they acted like this was a perfectly normal thing to ask.”

Bratman, who spent some years in his 20s on a commune working as an organic farmer and chef, knows firsthand how a healthy diet can become a pathological obsession. For years he was a strict organic vegetarian. “I only ate vegetables if they had come out of the ground in the last 15 minutes,” Bratman explains. He ate most meals alone so as to control exactly what and how much was being eaten. If he strayed from his diet, Bratman would experience self-loathing that could only be relieved by new extreme dietary restrictions. These purges were followed by an overwhelming sense of superiority towards those with less pure eating habits.

This self-destructive relationship to diet displays similarities to other eating disorders, in that food takes on a moral quality. But orthorexia is unique in that it has a positive element. “You are trying to be healthy,” Bratman explains. “Food takes on a luminous quality. It is aspirational.” Then perfectionism sets in, “because if adhering a little bit to the diet makes you healthy, adhering more makes you even healthier”.

This focus on “healthy” eating means that a person with orthorexic tendencies will not always have accompanying physical symptoms, like Ivy Thompson did. Bratman explains that even at his most obsessive he was still in good physical condition, which made it even more difficult to come to terms with what was a psychologically impaired relationship to food.

At age 19, Thompson had suffered a short and intense period of disordered eating, losing 17 kilograms in three months. “Those three months stuffed me up for a long time,” Thompson recalls. “I thought that being hungry was a good thing, that if I was hungry it meant I hadn’t overeaten. The Paleo diet helped me overcome some of my problems because it taught me that I could feel full and good if I ate the right food.” The waiter places a plate in front of her. It looks like a big breakfast, but instead of slices of toast there is a chicken breast.

After she was diagnosed with adrenal fatigue, Thompson identified cognitive patterns in her relationship to food similar to those that had been there when she was 19, except that her obsession had shifted from quantity to quality. Thompson reintroduced some carbs into her diet and started feeling better almost immediately. “It was a difficult time for me because I realised that strict adherence to any diet would never resolve my issues with food,” Thompson says, taking out her phone. “Sorry. Give me a second. I’m just going to Instagram my plate, because that’s what I do.”

In Thompson’s blog post about orthorexia titled ‘When Paleo Is One Obsession Replacing Another’ she suggests that, because the Paleo diet differs radically from most people’s food culture, maintenance of the diet requires perfectionistic dedication. Combine this with a history of disordered eating and an unshakeable belief in the diet’s ability to heal illness, and you have a recipe for orthorexic tendencies.

Dr Rebecca Reynolds, a psychologist and nutritionist who is conducting a study on the prevalence of orthorexia in Australia, says identifying orthorexic patients is extremely difficult because diagnostic tools are hard to formulate. This is part of the reason why orthorexia is not included in the most recent version of the Diagnostic and Statistical Manual of Mental Disorders (DSM–5). Without a formalised diagnostic process, Reynolds explains, it is hard to even estimate how many people are suffering from orthorexia.

Without accurate diagnosis, Bratman says, there is the concern that addressing orthorexia somehow undermines the importance of a healthy diet. This is an issue especially in the context of broader issues such as widespread obesity.

“There is a difference between a healthy-eating subculture and a psychological illness within it. I live on the west coast in the States. I have to be careful not to tell people I’m dating that I came up with orthorexia because they might accuse me of working for Monsanto.”

The idea that you can be more pure by eating purer food, that you can be spiritualised by a certain diet, is deeply woven into religious and cultural practices surrounding consumption – “let food be thy medicine”. In modern-day affluent countries, this food fixation is partly expressed in the form of gluten-free, super-food stickers in the health-food aisle at the supermarket. These contemporary obsessions, Bratman suggests, come from the same ancient roots. “We’re terrified of illness and death. People are not just suckers for dietary fads, they are enthusiastic suckers,” Bratman says with a smile. “They are begging to be deceived.”

Thompson neatly finishes off the last mouthful on her plate. “You know what? I feel better now at 34 with three kids than I did with no children when I was 20.” Does Thompson put her health down to her diet? “Absolutely 100%.” She pauses and checks her phone. “I’m still recovering from the year of low carb with Paleo. It pushed me. I’m depleted but it takes time to recover. Thanks to eating real food I’m doing remarkably well. I just bounce right out of bed.”

Rather than being organised into starters and mains, the menu at Palate restaurant in Melbourne is separated into six proteins and 15 vegetables. Ivy Thompson beckons the waiter. “I’ll have the herbed chicken breast,” she says, “and the grilled tomato, smashed avocado, sweet potato mash and sautéed spinach.”

Palate launched its Paleo menu in 2011, the same year Thompson started her Paleo diet. “I was 29 and had just had my third child in three years. I wasn’t happy with my weight, and I was suffering from chronic illnesses.”

Thompson came to her new eating regime via the blog Mark’s Daily Apple. Mark Sisson, a former endurance athlete from the US, promotes a “primal diet” based on what humans supposedly ate before food became civilised. It’s heavy on meat, nuts, fruit, vegetables and eggs, and there’s minimal dairy, wheat, starch and processed carbohydrates....